This invention relates generally to transformers and inductors, and in particular to picture frame matrix transformer and inductors.
The art of transformers and inductors of conventional construction is well known. A recent variant having a low profile is known as the "planar" transformer.
U.S. Pat. No. 4,665,357 "Flat Matrix Transformers" teaches the art of matrix transformers and inductors.
U.S. Pat. No. 4,845,606 "High Frequency Matrix Transformers" and U.S. Pat. No. 5,093,646 "High Frequency Matrix Transformers" teach embodiments of matrix transformers and inductors with improvements for high frequency excitation.
U.S. Pat. No. 4,978,906 "Picture Frame Matrix Transformer" teaches the art of matrix transformers and inductors comprising a plurality of elements placed end for end in a closed pattern. This patent also teaches that picture frame matrix transformers and inductors can be constructed in unitary structures resembling the well known "pot core" transformers and inductors.
The above patents are assigned to the same assignee as the present invention and they are incorporated herein by reference.
It is well known, but frequently overlooked, that the physical design of transformers and inductors is largely dependent on the thermal characteristics of the materials used in their construction. The magnetic core and the windings of a transformer or inductor generate heat in operation, and that heat must be conducted to ambient so that the temperature in the transformer or inductor does not exceed the temperature ratings of the materials of which it is constructed. Conventional transformers are usually chunky, and the thermal paths out of them are through multiple layers of insulating materials which often have poor thermal conductivity.
It is well known that as frequency is increased, the size of transformers and inductors can be decreased for a given volt-ampere rating, to a point. At higher frequencies, however, a number of significant losses come into play which arrest this trend, and may even reverse it. Within the conductors, skin effects and proximity effects increase the losses. Core losses also increase significantly with frequency, so much so that at some point the magnetic flux density may have to be derated so much that a design for higher frequency excitation may actually require a larger magnetic core.
Matrix transformers and inductors, and in particular picture frame matrix transformers and inductors, are very well adapted for high frequency operation, and they have superior thermal characteristics as compared to conventional transformers and inductors. Because there are few wires within any one element of the picture frame matrix transformer or inductor, proximity effects are essentially eliminated. The thermal paths are short, and the surface area to volume ratio is very high.
They may be spread out oven a larger area, so that the thermal loading is distributed.
Pot core transformers of conventional design have among the worst thermal characteristics, the windings being enclosed within the magnetic core. Heat conduction away from the windings is mostly through the magnetic core material, with a small amount conducted through the leads.